1. Field of the Invention
The invention generally relates to an imaging module capable of preventing foreign matter from attaching to a light-receiving surface thereof without degrading light receiving properties, a fabricating method for such an imaging module, and an imaging device having the imaging module.
2. Description of the Related Art
There are increasing demands on high density implementation of semiconductor components while growing demands on reduction in size and weight on electronic devices. Specifically, there are increasing demands on high integration of semiconductor imaging devices owing to advances in microfabrication technologies. In addition, various fabrication methods have been proposed for fabricating light-weight semiconductor imaging devices at low cost.
For example, a related art semiconductor imaging device includes a semiconductor imaging element having a light-receiving portion and a micro-lens configured to guide incident light to the light-receiving portion provided at an upper part of the light-receiving portion. The light-receiving portion and the micro-lens are covered with a low refractive index transparent material having a refractive index lower than that of the micro-lens. Further, an upper surface and side surfaces of the low refractive index transparent material are covered with a transparent material having hardness higher than that of the low refractive index transparent material. Accordingly, the semiconductor imaging element is packaged with double layers of the low refractive index transparent material and the transparent material having high hardness so as to prevent foreign matter from attaching on its light-receiving surface. That is, the semiconductor imaging element is covered with a transparent flat plate and side plates made of glass or resin to seal the entire semiconductor imaging element. As a result, foreign matter is prevented from entering into the semiconductor imaging element.
Similar proposals have been put forward with respect to preventing foreign matter from entering into the semiconductor imaging device. For example, Japanese Patent Application Publication No. 2006-295481 (hereinafter referred to as “Patent Document 1”) discloses such a technology to prevent foreign matter from entering into a semiconductor imaging device. Below, the related art semiconductor imaging device disclosed in Patent Document 1 is reviewed with reference to FIG. 13.
FIG. 13 is a cross-sectional diagram illustrating a configuration of the related art semiconductor imaging device 200. As illustrated in FIG. 13, in the related art semiconductor imaging device 200, a surface of a semiconductor substrate 201 includes an imaging region 202, a peripheral circuit region 203, and an electrode region 204. The imaging region 202 is provided with plural micro-lenses 205 and a semiconductor imaging element 206. The peripheral circuit region 203 is provided with a not-shown peripheral circuit. Further, the electrode region 204 is provided with a later-described electrode pad 207. A transparent member 208 is provided above the micro-lenses 205 with a predetermined gap. The transparent member 208 includes a planar shape that is larger than the imaging region 202, and is connected to outer frame portions 210 provided as spacers to form a hollow portion 209. As a result, the transparent member 208 is configured not to be brought into contact with the micro-lenses 205. A ultraviolet curable (UV-curable) adhesive 211 is applied on bonding surfaces of the outer frame portions 210 to be bonded to the peripheral circuit region 203 of the semiconductor substrate 201. In the related art semiconductor imaging device 200 having such a configuration, the transparent member 208 covers the micro-lenses 205 and the semiconductor imaging element 206 provided in the imaging region 202. The outer frame portions 210 connected to the transparent member 208 is bonded to the semiconductor substrate 201 with the UV-curable adhesive 211 so as to seal the imaging region 202. As a result, foreign matter is prevented from attaching to a light-receiving surface of the semiconductor element 206.
Further, like a pixel in an electronic imaging element including a CCD or CMOS, a polarizer may be arranged in front of the light-receiving surface of the imaging element to polarize light in a different polarizing direction in different regions. In this case, if the polarizer is arranged away from the light-receiving surface of the imaging element, adjacent pixels arranged near a boundary of different polarization directions of the polarizers may receive plural different polarization beams. This phenomenon is generally called “polarization crosstalk”. To avoid the polarization crosstalk, the polarizer may be arranged as close to the light-receiving surface of the imaging element as possible and the polarizer may be arranged such that a distance between the light-receiving surface of the imaging element and the polarizer may be kept constant without variability.
However, with the configuration of the related art semiconductor imaging device disclosed in Patent Document 1, it may be difficult to arrange the polarizer so close to the light-receiving surface of the imaging element, and to maintain the constant distance between the light-receiving surface of the imaging element and the polarizer without variability. The reason is as follows. As illustrated in FIG. 13, in the configuration of the related art semiconductor imaging device disclosed in Patent Document 1, the outer frame 210 is adhered to the semiconductor substrate 201 by applying the UV-curable adhesive 211 between the end of the bonding surface side of the outer frame 210 and the imaging region 202 and also between the end of the bonding surface side of the outer frame 210 and the electrode region 204. However, this adhesion of the outer frame 210 to the semiconductor substrate 201 may be difficult to be carried out by the above adhesion method of applying the UV-curable adhesive 211 between the end of the bonding surface side of the outer frame 210 and the imaging region 202 and also between the end of the bonding surface side of the outer frame 210 and the electrode region 204. In practice, the UV-curable adhesive 211 is applied to the end of a bonding surface side of the outer frame 210 at an opposite side where the transparent member 208 and the outer frame 210 are bonded. Thus, in the example of Patent Document 1, a total thickness of the UV-curable adhesive 211 may be 5 μm or more, that is, the distance between the light-receiving surface of the imaging element and the polarizer may have an additional distance of 5 μm or more. Thus, it may be difficult to arrange the polarizer as close as desired to the light-receiving surface of the imaging element. Further, the polarizer may be arranged with the constant distance based on the light-receiving surface of the imaging element as an origin between the light-receiving surface of the imaging element and the polarizer if the polarizer is arranged close to the light-receiving surface of the imaging element. However, the distance between the light-receiving surface of the imaging element and the polarizer may vary and thus not be constant due to inability to arrange the polarizer based on the light-receiving surface of the imaging element as the origin if the polarizer is arranged away from the light-receiving surface of the imaging element.
Another related art semiconductor image device is disclosed by Kawakami et al. in Proceedings of the 32nd Optical Symposium (Japan) (S. Kawakami et al., “Polalization imaging device utilizing photonic crystal polarizer”, Proceedings of the 32nd Optical Symposium (Japan), Optical Society of Japan, Vol. 32, July 2007; hereinafter referred to as “Non-Patent Document 1”). The related art semiconductor image device disclosed by Kawakami et al. is reviewed with reference to FIG. 14. As illustrated in FIG. 14, in the related art semiconductor image device 300, a CCD 302 is arranged on a semiconductor substrate 301 and a polarizer 303 is arranged on the CCD 302 such that a polarization surface of the polarizer 303 faces plural micro-lenses 304. Further, in the related art semiconductor image device 300, an adhesive 305 is supplied between the polarizer 303 and the micro-lenses 304 to securely bond the polarizer 303 and the micro-lenses 304. With this configuration, the polarizer 303 is arranged close to a light-receiving surface of the CCD 302. However, with this configuration disclosed in Non-Patent Document 1, the adhesive 305 is supplied between the micro-lenses 304 arranged above the light-receiving surface of the CCD 302 and the polarizer 303. This may interfere with incident light received on the light-receiving surface of the CCD 302. Thus, the adhesive 305 may cause optical distortion of incident light to drastically lower optical properties of the micro-lenses 304.